The present invention relates to an electrostatic microrelay which is driven by electrostatic attraction.
Conventionally, for example, there has been provided an electrostatic microrelay having a flat fixed electrode and a bent movable electrode (Japanese Patent Laid-Open Publication HEI 8-255546). In this electrostatic microrelay, by driving the movable electrode with electrostatic attraction that occurs with a voltage applied to between the electrodes, a movable contact provided at a free end portion of the movable electrode is put into contact, i.e. contact-making, with a fixed contact provided in the fixed electrode.
However, in this electrostatic microrelay, increasing the contact pressure at a contact-making involves suppressing the elasticity of the bent portion of the movable electrode to a small one. This would cause a problem that the opening force at a contact-breaking becomes smaller, resulting in deteriorated response characteristic. Conversely, increasing the elasticity at the bent portion of the movable electrode would necessitate a large driving force for the movable electrode to be attracted to the fixed electrode, which leads to a problem that the drive voltage must be increased. That is, the movable electrode is required to have two characteristics contradictory to each other, which could not be managed by the electrostatic microrelay of the above constitution.
The present invention having been accomplished to the above problems, an object of the invention is to provide an electrostatic microrelay which is good at response characteristic and which is capable of suppressing the drive voltage.
In order to achieve the above object, according to the present invention, there is provided an electrostatic microrelay in which a fixed contact of a base and a movable contact of a movable substrate are contactable with and separable from each other based on an electrostatic attraction generated with a voltage applied to between a fixed electrode of the base and a movable electrode of the movable substrate, wherein the movable electrode is evenly supported on the base via at least two elastic support portions.
With this constitution, when a voltage is applied to between the fixed electrode and the movable electrode opposed to each other, the elastic support portions are flexed by the electrostatic attraction, so that the movable contact and the fixed contact are put into contact with each other. Since the elastic support portions are provided in at least two in number evenly, the elasticity at each elastic support portion is a small one which acts evenly. Therefore, the movable electrode is smoothly attracted to the fixed electrode so that the movable contact and the fixed contact exhibits a stable, reliable contact-making. As a result of this, the contact reliability of the contacts is improved. Also, when the electrostatic attraction between the two electrodes is removed, the elasticity of the elastic support portion acts as a force for contact-breaking.
In the electrostatic microrelay as defined above, preferably, the elastic support portions are disposed so as to be opposed to the fixed electrode, in which case electrostatic attraction can be generated also between the elastic support portions and the fixed electrode so that the drive voltage can be suppressed.
Also preferably, the movable contact is supported on the movable substrate via a second elastic support portion which has an elasticity larger than the elastic support portion, in which case the contact reliability of the contacts can be further improved.
More specifically, with this constitution, with a voltage applied to between the fixed electrode and the movable electrode opposed to each other, the elastic support portions are flexed by electrostatic attraction, causing the movable electrode to be closer to the fixed electrode, with the result that the movable contact makes contact with the fixed contact. In this state, because the distance between the movable electrode and the fixed electrode is narrower than its initial state, an even larger electrostatic attraction acts for the attraction, causing the second elastic support portion to be flexed so that the movable electrode is attracted by the fixed electrode. Since the second elastic support portion is larger in elasticity than the elastic support portions, the movable contact makes contact with the fixed contact by a large load. Thus, without occurrence of any malfunctions due to vibrations or the like, the movable contact is put into a contact-making with the fixed contact at a desired contact pressure by the second elastic support portion. As a result, the contact reliability can be enhanced.
The elastic support portions may be implemented by at least two first beam portions extending sideways from anchors standing on the base, and the second elastic support portion may be implemented by a second beam portion obtained by at least one opening portion formed beside the movable contact of the movable substrate. In this case, the operating characteristics can be stabilized.
When the movable substrate is implemented by a single crystal silicon substrate, all the constituent members can be processed by semiconductor process, where variations in dimensional precision can be suppressed while a specifically life characteristic can be attained.
When the base is implemented by a glass substrate, the movable substrate formed of a single crystal silicon substrate can be integrated by anodic bonding, facilitating the assembly work. Further, capacitance among the fixed electrode, the fixed contact, interconnections and connecting pads on the base can be suppressed to low ones, so that high-frequency characteristics can be improved.